System for correcting sound records



Oct. 27, 1931. R. POMEROY I 1,828,941

SYSTEM FOR CORRECTING SOUND RECORDS OriginaI Filed May 22. 1928 5Sheets-Sheet i Inventor Rqyj Pomerg.

Y wk/w Oct. 27, 1931. R. J PC JMEROY 1,828,941

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SYSTEM FOR CORRECTING SOUND RECORDS Original Filed May 22, 1928' 3Sheets-Sheet 3 Patented Oct. 27, 1931 ROY J. POMEROY, OF LOS ANGELES,CALIFORNIA SYSTEM FOR CORRECTING SOUND'RECORDS Application filed May 22,1928, Serial No. 279,790. Renewed March 13,1931.

This invention relates generally to sound records, and is particularlyconcerned'with methods of perfecting the reproduction of sound. Thiscase is a companion to my ap -'5 plication entitled System forcorrecting sound records, Serial No. 279,789, filed on even dateherewith, and is directed to the same general subject-matter. Thesubstance of the present application may be considered as a variation ofthe specific steps of the method and system disclosed by the saidcompanion case, the broader claims generic to the common general methodbeing found appended to that case. i

ion case, the invention is broadly applicable to any record of soundvibrations, but is probably most conveniently illustrated. and describedin connection with the photographic type of record. The particular typeof photographic record with which I have chosen to illustrate theinvention consists of a shadedsband of constant density, a wavy outlinerepresenting the sound characterand volume. buch records, as well astheir method of recording and reproduction, are well known and need noparticular description here.

I11 reproducing sound from these records, distortion is alwaysintroduced by the vari- "ous units involved, this effect usually beingdue chiefly, however, to the speaker unit. Recording systems may beconstructed and balanced so as to introduce only a negligibly smalldistortion at most, and the main concern is therefore to eliminate thedistortions of reproduction. The chief concern is therefore with thedistortions, of reproduction.

It may now be stated as a general object of this invention toprovideam'eans for compensating for these distortions so that more erfectreproductionot sound will be 0b tainable.

The general method provides a Imethod 5 and's'ystem formakingadistortion corrected record, and this is done byintroducing, tothe record, correction distortions that are compensatory of, or havea-neutralizing eilect on, the distortions which .are introduced byreproduction. In the aforementionedcompan- As set out in the abovementioned compan-- duction.

ion case, this is specifically accomplished by what may betermed aphotographic method, in which an original photographic sound recordismade, and then reproduced as sound. The distorted sound thus obtainedis photographically recorded, this record being termed a distortionrecord. A negative i this distortion record is then photographicallycombined with a negative of the bined witha sound current representingthe original undistorted record, and this combination is so effectedthat the resultant current carries variations which represent only thediiterence between the two records, or in 7 other words, the distortion.A record of this current may be made upon a film and subsequentlyprinted above an original record, or may be directly made upon the filmcontaining the original record. In either case, the result is adistortion corrected record from whichsound may be finally reproducedwithout the. distortions of recording and repro- How this is done willbe better understood from the following detailed description of atypical means for carryingout the invention, reference for the purposebeing bad to the accompanying drawings, in which:

. Figure 1 shows a systemwfor making an original photographic soundrecord and a distortion photographic sound record;

Fig. 2 shows system for making a photographic distortion correctionrecord; Fig. '3 shows an original photographic sound record; g c l Fig.4 shows distortion photographic sound record Fig. 5 shows a photographicdistortion correction record Fig. 6 shows aphotographicdistortioncorrected record; I

Fig. 7 shows a variational system for making a photographicdistortion-correction record; and

Fig. 8 shows a system for making a photographic distortion-correctionrecord'directly upon a film having an original record.

With reference to Fig. 1 the microphone M1 is connected through theleads 10, 11 to the amplifier A1. Amplifier A1. and other amplifiers tobe mentioned, may be any suitable electrical or vacuum tube amplifiersadapted to amplify an audio-frequency electrical current. The output 12,13 of amplifier A1 is connected to a glow tube G1, or other lightvarying device before which travels a film 14. A plate having a slit S1is interposed between the glow tube and the film.

A second plate having a slit S2 is positioned opposite the glow tube,and beyond it is a photoelectric cell P1. Leads 15, 16 from thephotoelectric cell P1 connect to the switch 17, and from there continueto the amplifier A2. Leads 18, 19, having therein a switch 20, connectthe-microphone leads 10, 11 with the photoelectric cell leads 15, 16 ata point between the switch 17 and the ampifier A2. The output leads 22,23 of the amplifier A2 connect to the speaker H. The system of Fig.

1 may be operated in either of two manners, depending upon the positionsof switches 17 and 20. The system will first be described with switch 17closed and switch 20 open, the operation with the switches reversed fromthese positions being considered later.

Microphone M1 picks up the original sound, a sound current beingconducted therefrom by the leads 10, 11 to the amplifier A1, and thenceto the glow tube G1, the traveling fihn 14: taking a positive soundrecord P0 of the original undistorted sound. A positive photographicrecord, in the terminology herein employed, is the original photographicrecord obtained in recording sound. A negative record is the reversal ofthis positive, or in other words is the record which woud be obtained byordinary light printing from a positive record. The record P0 actuallycontains distortions introduced within the re cording system, but theseare capable of being reduced to negligibleproportions by properlydesigning the recording system, and the distortions of recording maytherefore be disregarded for the purpose of the present discussion.Light rays are also transmitted from the glow tube through the slit S2and affect the photoelectric cell P1. Switch 20 being open and switch 17closed, modulated sound current from the photoelectric cell is conductedby the leads 15, 16 into the amplfier A2 where they are amplified, theamplifier current passing to speaker H and there being reproduced assound.

From this point, the description of the various units may beconveniently accompained by a brief explanatlon of their operationwithin the system, and this plan of exposition will hereafter befollowed.

Sound reproduced by the speaker H is picked up by microphone M2, a soundcurrent being conducted therefrom through the amplifier A3, and afteramplification being conducted to the glow tube G2 before which travels afilm 21. A plate having a slit S3 is interposed between the glow tubeand this film. The film 21, which travels at a speed synchronous withthat of film 14, thus takes a positive sound record Pcl identical withthe positive sound record P0 upon film 14 but with the addition of thedistortions introduced in reproduction, and also with the relativelynegligible recording distortions of the system M2, A3, G2, S3. Thereproducing system Pl, A2, H, must be one having identicalcharacteristics with the one which is to be used in final reproduction,and the recording system M2, A3, G2, S3 is one having identicalcharacteristics with the original recording system M1, A1, G1, S1, orone introducing little or no distortion. While it was stated above thata positive record Pd is obtained upon film 21 in the system of Fig. 1,whether a positive or a negative is actually obtained depends uponseveral factors, such as the polarity of the photo-electric cell P1 andmicrophone M2 with respect to their amplifiers. To avoid confusion thesystems will therefore be assumed in all cases throughout thespecification, unless otherwise stated, to be so aranged that a soundwave representation passes through the system without reversal from apositive sound record representation to a'negative sound recordrepresenta tion, or vice versa. It will be understood, however, that thesteps of the method may easily be varied by such reversals and bycorresponding variations in the printing operations, as hereinafterindicated. All such variations, of course, lie within the scope of myinvention.

' While the records P0 and Pd are produced simultaneously in the systemof Fig. 1, in effect, the making of Pd is the same as if it were made byreproduction of P0.

In Fig. 3 is shown the film 14 with the original sound record P0 havinga wavy outline 30, the record being shown greatly enlarged for thepurpose of expressing more clearly the various relations between therecords. A record of a continuous uniform sound is chosen forrepresentation in the diagram merely for the sake of simplicity ofillustration, it being understood that the method applies in the samemanner to the record of a complex sound wave. In Fig. 4 is shown thefilm 21 with the record Pd. This feeei-d is similar to P0, but hasimposed upon it all of the distortions introduced in reproduction.

,record, and its outline 31 as the distorted curve. This distorted curve31 is shown superposed Iin dotted lines upon the positive ,record P inFig. 3, and it will be seen that the distortion introduced in thereproducing system at any point in the recordis reprecurves 3(land 31. Vc Whether the amplitude of the distorted curve-31 is greater or lessthanthat of the -original curve 3O depends upon the characteristicsofthe reproducing units, and in.

any specific case maydepend upon the varying factors of sound character.

For instance, at one frequency. the distorted curve-31 may be of'a,greater'amplitude than the original curve 30, another frequency it maybe less,

.while 'at some intermediate frequency the curves may coincide,indicating that at this frequency :no distortional effect is obtained.

"For the sake of simplicity, only the casein which the distortion effectcausesan increase iirthesound waveamplitude is illustrated inthe-drawings. It will later be apparent that althoughthe distort-ionmight equally as well cause adecrease inamplitude, the operation ofthesystem is similar ineither case, and.

therefore, for-the sake of simplicity of explanation, the operation willlie-explained with reference to the aforementioned arbitrarily. chosencase; it being understood that the total ,resultantdistortion introducedin reproduction:inay, cause either an increase or decrease in; theamplitude of the sound wave, and that the system corrects the record ineither case; .In other words,lthe distortion may-he either'minus or pluswith respect to the original record, I

The positive record P0 is nextto be artificially modified by therelative addition of opacity at those points at which'thedistortioniisrelatively minus, .or at which the dis- .torted curve 31 falls below theoriginalcurve '30, andby the relative subtraction of opacity at thosepoints at which the distortion is relatively plus, orat which thedistorted curve .31 rises above the originalcurve 30, the

, amount ofthis modification at any point being always equal to thedistortion at that point. 7. A simple manner of viewing these relations.is that the modified record is to be made relatively as much moreopaquethan the-original record as the distortion record is less opaque thanthe original record, and vice versa, as the case may be; i

If then this modified record is run through a reproducing system havingthe same char- Iacteristics as the one utilizedji-n making the modifiedrecord, the distortions introduced by that system will again be addedand subtracted in the same sense or directions as before; but now thereproducing system causes the sound wave ofthe modlfied record to bealtered within the system to the shape and proportions of the originalwave, and distortionless audible reproduction of the original sound isobtained. J

The method of'doing this will now be deiscribed, and reference forthispurpose will record Pd is run'throughan identical system;

consisting of illuminant I, slit 43 and photoelectric cell 44. These twosystems must be matched to have substantially identical characteristics,and thefilms 14 and 21 must be synchronously driven. The photo-electric;cells 42 .and44are then differentially connectedby the leads 45 and 46,so that the current flowing in circuit 45, 46 is the diiference of thatgenerated by the photoelectric cells 42 and 44, and thereforerepresentsthe difference in the records P0 and Pd, or in other words thedistortion. For the purpose of relatively balancing potentials, as willlater be vmore fully explained, .potentiometers and 56 are providedacross the photo-electric. cells 42 and 44, respectively. In series withcircuit 45, 46 is a circuit 47, 48 leading to the amplifier A4, theoutput current of which is conducted to a glow tube 49 andphotographic-ally recorded upon the film 50, aslit 51 beingprovidedbetween the film and the glowtube. A distortion-correctionrecord C, shown in Fig- 5, is thus obtained, the outline 52 of whichrepresents the distortion.

'l/Vith the system in balance, the differential distortion-currentflowing inthe circuit 47 48 into amplifier A4 is a wavy outlinedalternating current. The output of theamplifier A4 then consists of adirect current with an amplification of the wavy outline of the distortion current impressed upon it. It will thusbe apparent that Whethera peak or a depression in the final outputcurrent wave. andcorrespondingly 1n the correction record 0, results from any particularhalf-cycle of the amplifier input distortion-current de- .pends upon howthe leads 4'7 and 48 are connected into the am'plifier'A4. Arbitrarilypeak in the correction record G corresponds to peaks in the original anddistortion positives P0 and Pd, as clearly shown in Figs. 8, 4and5, afilm 53 is then printed along one edge with a negative correction recordC of the record C just obtained, and with the originalpositive P0 alongthe other, as shown in Fig. 6, care being taken that the two prints,

the original record and the correction record,

, choosing for illustration the case in which a sidered as having itsinput leads reversed from the arrangement of Fig. 2, as above stated,thus giving the negative C rather than the positive C. In the caseillustrated, the correction record C is madedirectly upon film 53, thisfilm having apreviously printed original record P0. Or, if desired,record C may be made upon a blank film, and by subsequent printingoperations, later combined with an original record P0.

As the sound character is determined solely by the outlines of therecords, the tow records may be laterally positioned upon the singlefilm in any convenient manner which insures absence of overlapping.

We have now added to the original record a correction band of opacitywhich varies in width by the amount of the distortions, and in adirection or sense negative to that of the distortions. Stated withreference to Fig. 3, we have relatively added opacity by the amount ofthe distortions where the distorted curve 31 falls below the originalcurve 30, and relatively subtracted opacity by the amount of thedistortions where the distorted curve 31 rises above the original curve30. Another manner of expressing this is that we have relatively addedopacity to the original record iy the amount of and negatively to thesense of the distortions.

The result of running the distortion-corrected film 51 through thereproducing system will then be that the distortions inherentlyassociated with the reproducing system will act to correct the soundwaves represented by this oppositely distorted record, changing themback to the original wave shape and proportions, and thus the originalaudible sound is reproduced without distortion.

In order that the above system be operative, it is essential that theamplifiers of the recording and reproducing systems of Fig. 1 be sopotentiated or balanced against one another that the sound currentsobtained from the records P0 and Pd in the correction record makingsystem of Fig. will at any point be of the same magnitudes, except forthe distortional difference between them, and will therefore exactlyneutralize one another except for this distortierr-representing current.

This balancing may be accomplished as fol lows: In the recording andreproducing system of Fig. 1,'there' will be at least onefrequency ofsound current at which no distor tion will be introduced inreproduction. This frequency being ascertained, it is induced in thesystem, and the system is then balanced and permanently set atpotentials which will give identical records P0 and Pd under thoseconditions of current frequency. With the system so balanced, a soundcurrent of any frequency at'which distortion is introduced will make arecord Pal exactly like the original undistorted record P0 except forthe distorabove mentioned frequency at which no distortion occurs, andthese are reproduced as sound currents in the system of Fig. 2. If theentire system is in balance, there will be no resultant current in thecircuit 45, 46 and no further adjustment is necessary. If,

however, the balancing is not perfect, it may be made so by adjustingthe potentiometers 55 and 56 in the circuit 45, 46 until the resultantcurrent is reduced to zero. The system is then in balance and readinessfor operation. The test for this condition is that there shall be nosound current in the circuit of glow tube 49.

The system has so far been described as compensating solely for thedisabilities .of reproduction; but the system actually compensates forthe relatively small disabilities of recording as well, as will now bepointed out. Starting at the microphone M1 in Fig. 1, the sound waverepresentation, after passing through amplifier A1 and being transformedfrom a modulated electric current to modulated light waves, has becomedistorted by the elements of the recording system, and

the original sound record P0 therefore contains these distortions. Thesound current picked up by the photo-electric cell P1, which currentalso has these recording distortions, is passed through the amplifier A2and, with the additional distortions of repreduction, is reproduced assound. The distorted sound is then picked up by the microphone M2,passed through amplifier A3, and, with the additional distortions of therecording system, is recorded. The record Pd thus con tains thedistortions of the original recording, the distortions of reproduction,and the distortions of the second recording; while the record P0contains only the distortions of the original recording. Thedifferential correction record C made from these two records thencontains their difference, or the distortions of recording plus thedistortions of reproducing; and the record P0 modified by the record Cis therefore corrected for the recording distortions which it containsand also for the reproduction distortions which will be introduced insubsequent reproduction. Both the recording and reproducing systemsutilized to modify the record must of course, be the same, or haveidentical characteristics, as the ones used originally in recording andin finally reproducing the sound.

In case the recording distortions are negligible, the system may besimplified by utilizing an arrangement such as is obtained in correctionis made for the units'Al, G1, and,

P1, their distortions being regarded as relativelyinsignificant.

If desired, instead of making P0 and Pd originally, record P0 may bemade originally, and by properly passing it before the photo-electriccell P1 of the system of Fig. '1, it may be reproduced as a soundcurrent, amplified, .and photographically recorded. That therecord soobtained be a positive Pd, the polarity of the photo-electric cell P1may be reversed with respect to its amplifier from its arrangement inthe'system of Fig. 20"

1. Or a negative of positive Pb may be passed before the photo-electriccell to give thepositive Pd. Other variations designed to producepositives P0 and Pd for'use in the system of Fig. 2 (01 correspondingnegatives, which are equally adapted) will be readily apparent. I

*It will now be shown howcertain of the steps may be eliminated,reference for this 1 purpose'being had to Fig. 7. The circuit here shownhas parts similar to that shown in Figs. 1 and 2, and like parts of thesystems are therefore indicated bylike numerals. Leads "and 61 areconnected from the output leads 12, 13 of amplifier A1 to the, outputleads of amplifier A3, and these leads are differentially connected sothat, except for the distortion-current, the sound currents in circuit60. 61 are neutralized. Potentiometers 64 and 65 are connected in thiscase across the outputs of amplifiers A1 and A3 respectively for thepurpose of balancingthe amplifier potentials, similarly to the mannerpreviously explained;

In series with circuit 60, 61 are leads 62, 63 leading to the amplifierA4, the output of which connects to the glow tube 49, as before.

A correction record G is thus directly obtained upon the film 50simultaneously with the making of the original record Po, thus doingaway with the necessity for making record Pd. A negative correctionrecord G of this record C is then printed with the original record P0,as before. Or the system may easily be arranged (by merely reversing theinput leads to A4, for instance) to give the correction record Coriginally, and by then properly positioning glow tubes G1 and 49,original record P0 and correction record C may be originally andsimultaneously printed in proper register upon a single film, thusgiving the distortion corrected record at once.

The invention has thus far. been described as correcting for orcompensating the distortions occurring 1n the simple recordation andreproduction of any typlcal sound rec- 0rd. The broad invention,however, has numerous applications in furtherance of this specific use.For instance, it may be embodied as applied to a" correction of thedistortion effects otherwise unavoidably introduced in radiobroadcasting. For this purpose, sound would be broadcast fromsound'records in V which compensation has been made for the distortionsintroduced in their making and reproduction, and also for thedistortions in-.

troduced by the radio broadcasting set, and by the average radioreceivin' equipment,

While I have illustrated the invention with the aid of a constant.density, variable outline sound record, it will be apparent that theessence of the invention is not limited to the relativeaddition andsubtraction of bands of varyingwidth, but may be considered; whenapplied to photographic records, as involving the addition andsubtraction of opacity, and therefore any type of photo'- graphic soundrecord is responsive to the method. In its broadest aspect, inwhich is Iembraced all forms of sound records, it may be considered as involvingthe altering of the elements making up the original sound record by therelative addition of correction distortions in the amount of,'and in anopposite sense to, the distortions introduced in recording andreproduction.

it will be understood that the foregoing drawings and description aremerely illustra tive of and not restrictive upon the invention in itsbroadest sense,-for various changes in the specific method and systemmay be made withoutdeparting from the spirit and scope of the broaderclaims appended hereto.

l. The method of modifying sound records that includes, makin anoriginal record of audible sound, an ibly reproducing the sound with thedistortions of reproduction, making a distortion record of the distortedsound as soreproduced,synchronously producing electrical sound currentsfrom the original and the distortion records, difleren tially combiningthe sound currents so obtained in such a manner that the sound currentsare neutralized except for a distortion representing current, making acorrection record of the distortion-representing current, and makingfladistortion-corrected record by modifying the original record with thecob rection record in such a manner as to alter the original recordby'the amount of and in a sense opposite to the distortions introducedin reproduction.

2. The method'of modifying sound records records, differentiallycombining the sound currents so obtained in such a manner that the soundcurrents are neutralized except for a distortion-representing current,making a photographic correction record of the distortion-representingcurrent, and making a photographic distortion-corrected record bymodifying the original record by the correction record in such a manneras to add opacity to the original record varying in quantity by theamount of and in a sense negative to the distortions introduced inreproduction.

3. The method of modifying sound records that includes, simultaneously,making an original photographic sound record, audibly reproducing soundwith the distortions of reproduction, and making a photographicdistortion record of the distorted sound as so reproduced; synchronouslyproducing electrical sound currents from the original and the distortionrecords, differentially combining the sound currents so obtained in sucha manner that the sound currents are neutralized except for adistortion-representing current, making a photographic correction recordof the distortion-representing cur:

rent, making a photographic distortion-corrected record by modifying theoriginal record by the correction record in such a manner as to addopacity to the original record varying in quantity by the amount of andin a sense negative to the distortions introduced in reproduction.

4. The method of modifying sound records that includes, making anoriginal photographic sound record, audibly reproducing sound with thedistortions of reproduction, making a photographic distortion record ofthe distorted sound as so reproduced, synchronously producing electricalsound currents from the original and the distortion records,difierentially combining the sound currents so obtained in such a mannerthat the sound currents are neutralized except for adistortion-representing current, making a photographic correctionrecordof the distortion-representing current, making a photographicdistortion-corrected record by printing a film with an original recordand 159. with the correction record, in a manner that opacity is addedto the original record in a quantity varying by the amount of andnegatively to thesense of the distortions introduced in reproduction.

5. The method of correcting sound records that includes, producing anelectrical sound current from the original sound, making an originalphotographic sound record from the sound current, audibly reproducingsound 9", corresponding to the said sound current, this sound having thedistortions of reproduction, and making a photographic distortion recordof the distorted sound as so reproduced, synchronously producing soundcur- :rents from the original and the distortion records, diiferentiallycombining the sound currents so obtained in such a manner that the soundcurrents will be neutralized except for a distortion-representingcurrent, making a photographic correction record of thedistortion-representing current, making a photographic distortioncorrected record by printing a film with an original record and With thecorrection record, all in a manner that opacity is added to the originalrecord varying by the amount of and negatively to the sense of thedistortions introduced in reproduction.

6. In a system for correcting sound records, means for producing anoriginal electrical sound current from the original sound, photographicsound current recording means actuated by the said original soundcurrent, means for reproducing sound with the distortions ofreproduction from the sound current, means for producing a distortedelectrical sound current from the distorted sound, photographic soundcurrent recording means actuated by the said distorted sound current,means for producing a distorted electrical sound current from thedistortion photographic sound record so produced, means for producing anelectrical sound current from a photographic sound record made of theoriginal sound current, 95 means for diiferentially combining the lastmentioned sound current with the above said distorted sound currentproduced from the distortion record in such a manner that the parts ofthe sound current waves representing the original sound are neutralizedleaving a distortion-representing electrical current, and photographicmeans for recording the distortion-representing current.

In Witness that I claim the foregoing I have hereunto subscribed my namethis 24th day of March, 1928.

ROY J. POMEROY.

